Field of the Invention: This invention relates to power tongs for making up or breaking apart the drill tools used in oil and geologic drilling engineering and is particularly adequate for make-up and break-apart operations on drill pipes, drill collars and kellys. The power tongs includes an upper tong and a lower tong each being swivelly connected with the other. Each tong is provided with a pair of hydraulically or pneumatically powered tong dies being capable of moving toward or away from each other synchronously to grip or release drill tools.
Description of the Prior Art: Conventionally, suspended B-type tongs have been used in oil drilling engineering as the equipment for making up or breaking apart drill tools. Their operations concern hazardous and heavy manual labour, and various types of power tongs have then been developed to replace some of the operations of B-type tongs. Among these power tongs, the representative ones are TW-60 model produced by U.S. company Varco and that made known to the public by the U.S. Pat. No. 4,060,014. Their common feature consists in accomplishing the make-up and break-apart tasks with large torques, excluding the function of completing the same mission with small torques unless they are used in combination with a separate spinner having the above-mentioned function. The main disadvantages of existing power tongs are as follows:
1. A hand-operated latching door or similar fittings provided at the mounth of each tong. PA1 2. Operations for replacements of components needed when the sizes of drill tools vary; no automatic adaptability to this variation. PA1 3. More limitation to the eccentric wear of joints of drill tools. PA1 4. More complexity and massiveness. PA1 5. More valves needed when operated and hence less effectiveness presented. PA1 6. A special system for moving the power tongs such as a power hoist or a moving pedestal needed.